Process of making cyanids.



No. 792,259. PATENTED JUNE 13,1905. J. GROSSMANN.

PROCESS OF MAKING .CYANIDS.

APPLICATION FILED APR. 16, 1903.

No. 792,259. Patented June 13, 1905.

UNITED STATES PATENT OFFICE.

JACOB GROSSMANN, OF HARPURHEY, MANCHESTER, ENGLAND, ASSIGNOR TO GROSSMANNS CYANIDE PATENT$ SYNDICATE, LIMITED, OF HAR- PURHEY, MANCHESTER, ENGLAND.

PROCESS OF MAKING CYANIDS.

SPECIFICATION forming part of Letters Patent No. 792,259, dated June 13, 1905.

Application filed April 16, 1903. Serial No. 152.952.

T (1/71 wh m i TIMI/y 6071106177111 The reaction which is supposed to take place Beitknown that I, J AGOB GRossMANN, acitibetween dilute Sulfuric acid and ferrocyanid zen of (JrreatBritain, residing at IiIarpurhey, of potash is generally represented as follows:

Manchester, in the county of Lancaster, Eng- (1) 2KiFeGy+(3+w)H2SO*: 5o

5 land, have invented certain new and useful Im- 1 I provements in and Connected with the Manu- 6Hby+lhFezbyb+gKyzsorkmHzSOi facture of Cyanids, of which the following is in which 1: represents any figure up to three. a full, clear, and exact description. Thus one half of the total cyanogen should be It has been known for many years that on made available as hydrocyanic acid for the I0 distilling two molecules ferrocyanid of potash preparation of cyanids, While the other half with from three to six molecules dilute sulshould be obtained in the form of the insolufuric acid hydrocyanic acid is evolved and an ble compound which is generally termed Evinsoluble compound containing cyanogen and eritts salt; but this reaction does not take calle( Everitts salt is formed. It has also place regularly according to the equation, and 5 been known for many years that the Everitts therefore varying quantities of hydrocyanic salt thus produced maybe partly reconverted acid are evolved. I have, however, ascerinto ferrocyanid of potash by boiling with tained that whatever the yield of hydrocyanic caustic alkali; but no method was known acid the resulting Everitts salt contains exwhereby these isolated reactions could be comactly the amount of cyanogen corresponding 5 bined in such a manner that they would ultito the difference between the total cyanogen mately yield all the cyanogen contained in originally contained in the ferrocyanid and ferrocyanid of potash as hydrocyanic acid in that evolved as hydrocyanic acid in such a practically quantitative proportions, nor was form that it can be practically quantitatively it known that other ferrocyanids besides the reconverted into alkali ferrocyanid. .I have, 7 5 potassium ferrocyanid follow the same law. moreover, foundthat for the purpose of my By experimenting on a commercial scale with process two molecules of ferrocyanid to three large quantities of material and under such molecules of sulfuric acid (with about five per conditions as are the only practicable ones in cent. of the latter in excess) are most practidealing with such a poisonous substance as hycable, as the waste liquors are almost neutral. 3 drocyanic acid on alarge scaleIhave been able The equation which is given in text-books to devise a method and plant by which I can as representing the action of alkali on Evermanufacturc cyanids of good commercial qualitts salt is as follows: ity by distilling ferrocyanids with sulfuric I A r acid, absorbing the prussic acid evolved in al- (2) K2Fe2by"+2KOIIk*Fe(JyG+Fe(OH)2 35 kali,and reconverting the Everitts saltformed i. 0., ferrocyanid and ferrous hydrate are into ferrocyanids in such a manner as to pracformed; but the quantity of ferrocyanid retically obtain allthe cyanogen contained in ferconverted is far below theory unless a large rocyanid without loss as cyanid of potassium, excess of caustic be used and boiling prosodium, calcium, or similar compounds. I longed for an impracticable time, while the 5 4 have, moreover, worked out the proportions of air is excluded, so as to obtain the ferrous the substances employed and the dilution of hydrate according to the equation; but I the liquids in such a manner as are most ecohave found that if care is taken to supply nomical and suitable for the preparation of cysufficient air during the boiling to produce anids from ferrocyanids by distilling with sulnot the ferrous hydrate, but a higher oXid of 45 furic acid, and particularly so for the cycle of iron, this reaction takes place quantitatively operations which I have designed. with a very small excess of caustic alkali and in a very short time. My reaction is therefore as follows:

Everitts salt may also be converted into ferrocyanid by boiling it with solution of carbonate of alkali by itself or mixed with caustic alkali in the presence of air in excess, or boiling it with an alkaline earth in conjunction with a solution of a carbonate of alkali in the presence of air in excess, or by boiling it with an alkaline earth and water in the presence of air in excess and subsequently decomposing any single or double salt of an alkaline earth formed with alkali carbonate.

The conversion of the hydrocyanic acid into cyanid of potassium may be expressed by the equation As long as the temperature does not rise too high the absorption of the hydroeyanic acid by caustic-alkali solution is almost complete. I find the same to be the case with caustic lime or milk of lime, which produces calcium cyanid.

It will be seen from equation (1) that during the distillation of hydroeyanic acid an equivalent quantity of sulfate of potash is formed, and l have found that if the hydroeyanic acid evolved be absorbed in milk of lime the cyanid of calcium thus produced can be converted into potassium cyanid by mixing with the solution of potassium sulfate obtained as above, or the slaked lime maybe mixed with the solution of potassium sulfate and the mixture used for absorbing the hydroeyanic acid, when the formation of calcium cyanid and its conversion into potassium cyauid take place simultaneously. The resulting potassi um-cyanid solution may be separated from the precipitate of calcium sulfate by decantation or filtration. Sodium sulfate or a mixture of this and. potassium sulfate gives analogous results.

I. have also found that sodium ferrocyanid behaves exactly like the potassium ferrocyanid as regards the evolution of hydrocyanic acid and as regards the relation in the composition of the resulting sodium Everitts salt and the quantity of hydroeyanic acid evolved. Mixtures of potassium and sodium ferrocyanid also behave analogously. So do double salts, such as calcium-potassium ferrocyanid and similar compounds.

1 have also found that caustic soda behaves analogously to caustic potash in the conversion of Everitts salt into ferrocyanid. So do mixtures of caustic soda and potash.

it appears from the foregoing that my invention comprises a combination of the following operations: First, distillation of hy- E drocyanic acid; second, absorption of the hydrocyanic acid and further treatment of the resulting cyanid solution; third, reconversion of the Everitts salt. These operations are carried out on a large scale as follows:

Ill/wt. Distal/ration of h (lroc rmic m;/f(l.- I have found that lead is not acted on either by the mixture of ferrocyanid and sulfuric acid or by hydroeyanic acid, and I therefore prefer to carry out this operation in a still made of lead; but enameled iron or other suitable material may be used forits construction when it is advisable to do so. Separate pipes for the snpplyof live steam, air, sulfuricacid, and ferrocyanid solution go to the bottom of the still, which may also contain a steam-coil for heating by confined steam. It is connected at the top with a dephlegmating or fractionating apparatus, which may be cooled by water, cold air, or otherwise. I have found that the vapor of hydroeyanic acid does not act on iron, and the dephlegmating arrangement therefore can be made of that material. Pipes lead from the dephlegmating apparatus to a number of absorbing vessels made of iron or other suitable material and litted with suitable agitatingmachinery. The whole system is at its outlet connected with a Kin-ting exhauster or similar apparatus for producing a partial vacuum or for drawing air through under a partial vacuum or otherwise.

A suitable apparatus to be preferably used for the distillation of the hydroeyanic acid is shown in the accompanying drawing.

Ais a still, preferably made of lead; a and c are pipes leading from the storage vessels (J and D into the still and convey sulfuric acid and the solution of ferrocyanid, respectively, into that still. For heating the still live steam is conveyed to it by the pipe 1), whereas the still is emptied by means of the runningoff pipe (I. The hydroeyanic acid evolved passes through the dephlegniating or condensing tower B, whence it goes forward first into the absorption vessel E, thence into the absorption vessel F, and finally into the absorption vessel 7, all of which are charged with a solution of caustic alkali. The last traces of hydroeyanic acid are retained in the vessel with perfect .a'fety.

H is a Korting injector connected to the last absorbing vessel, by which a partial vacuum is produced which is maintained in the whole apparatus while the process of distillation is going on.

hen an operation is commencing, the necessary quantity of hot saturated solution of ferrocyanid of potash containing about twenty-live per cent. of crystallized ferrocyanid is run into the still, (which in a continuous process will be still hot from a previous operation.) All the taps are closed and the exhauster is set to work, so as to keep upa partial vacuum of about four inches of mercury. The taps for live and confined steam are then turned on and the acid, which'contains about twenty-five per cent. H2801, is run in slowly at the rate of about one gallon per minute or slower. The quantity of acid used is about three per cent. to five per cent. in excess of the quantity necessary to form the three molecules of neutral potassium sulfate, corresponding to two molecules of ferrocyanid. The apparatus works very regularly, and when once it has been ascertained how long it takes to finish an operation it will be found that subsequent operations under the same conditions will finish in the same time. The ferrocyanid used should be reasonably free from carbonates, sullids, and other ingredients which may either interfere with the reaction in the still or influence the quality of cyanid produced.

Several stills supplied with overflows and suitably connected may be combined in such a manner as to work continuously.

During part or the whole of the operation a current of air heated or otherwise may be passed through the still.

01 0012 (1. x T/MUIYM'I OH of z /w fiy (lrocyan 0 (00M rnul 7"urf/m' tmuzmmt of the vvzsuhfing cycmz'cl .w1/'/IZ"2i/u/..Fl1e absorption vessels are closed boxes or pots, made of iron or other suitable material, fitted with agitating machinery and of such size that they will hold sufficient alkaline liquors to condense the hydrocyanic acid and the vapor evolved from four or more still operations. Two, three, or more of these vessels are arranged in series, preferably at increasing heights, so that the liquid from the higher can be drawn into the lower vessel or vessels. The hydrocyanic acid enters the lower vessel first, is taken to the bottom, the gas leaves through a pipe at the top and is drawn through the box or boxes at a higher level in the same manner. The boxes are charged with a solution of caustic soda, caustic potash, or a mixture of both. I If it is desirable to produce calcium cyanid, they may be charged with milk of lime, and, further, slaked lime may be added after one or several operations; but in every case care must be taken that there is always slight excess of free caustic and never any free hydrocyanic acid. If it is desired to use sulfate of potash or soda or a mixture of both, the respective solutions may be mixed with slaked lime, the mixture charged into the absorptionpots, and further quantities of lime and sulfate, the latter either in concentrated solution or in the solid state, may be added after one or several still operations. The temperature is regulated by cooling the absorptionpots. It is advisable to keep it below 40 centigrade. \Vhen the first absorbing vessel is suiliciently saturated with hydrocyanic acid, which is ascertained by test, its contents are run off into suitable covered tanks, and the pot may be recharged. WVhen soda or potash has been used for absorption, no furposed.

ther treatment is required, nor when lime has been used for absorbing for the purpose of making cyanid of lime for use as such in solution; but when cyanid of lime has been made as an intermediate product and has to be converted into the potassium or sodium compound it is decomposed by its equivalent or an excess of sulfate of potash or soda or a mixture of both. WVhen a mixture of sulfate of alkali and lime has been used for absorbing, the resulting mass is practically of the same composition as the calcium cyanid and sulfate of alkali mixture mentioned above. The mass in either case is left to settle in closed vessels, guarded against access of air and light, and the liquor separated from the precipitate by decantation and the latter washed, or the filtration and washing may be carried out by means of a centrifugal machine or a filterpress. The resulting liquor, which contains sulfate of lime, soda, and potash, besides cyanid, may be purified by the addition of carbonate of alkalis or by the successive addition of cyanid of barium and carbonate of alkali or by any other means well known and apparent to chemists. The liquors, purified or otherwise, obtained by either of the above means may be concentrated or madeinto solid by boiling down in a suitable vacuum-pan. Whenever lime has been used for absorption, care should be taken that no cyanid of calcium as such may be conveyed to the vacuum-pan or may form in the process of evaporation.

Third. Recmwev as"! 011/ Q the 11 1mm tzfs salt.- The contents of the still after distillation is linished are run into tanks and the solution of alkali sulfate separated from the Everitts salt by decantation or filtration. The alkali sulfate, which is slightly acid, is neutralized by means of calcium carbonate, alkali carbonate, or other suitable means, and may then be further purified and afterward concentrated by boiling down, crystallizing, or fishing. The Everitts salt, which need not be quite free from sulfate, is made neutral by means of alkali carbonate or caustic alkali and mixed with the equivalent quantity plus about five per cent. of caustic soda or potash or a mixture of both or of carbonate of alkali. It is heated in suitable vessels and of such capacity as will contain the large quantity of froth which is produced during the operation, either by steam or other means, to boiling, is violently agitated, and air is passed through by means of a compressor or steam-injector until a test shows that all the Everitts salt has been decom- The air may be heated or otherwise. WVith some experience the time necessary for this can be fixed approximately for each operation after a few trials. The color of the precipitate of iron produced should be brownish black when the operation is finished. The resulting solution of alkali ferrocyanid may be separated from the iron com pound by decantation or filtration and the IIO latter washed free from ferrocyanid. The acid and Everittssalt are produced, and I resulting ferroeyanid solution is carefully neu tralized with suitable acid or by other means and may go back into the process either as solution or it may be further concentrated or boiled down and crystallized.

Instead of passing air through in the manner described the equivalent of agitating violently in presence of air, so as to expose the whole to its action, may be adopted, but not so advantageously.

Instead of using caustic alkali; carbonate of alkali, a mixture of carbonate and caustic alkali, may be used in equivalent proportions, or alkali earths, such as milk of lime and carbonate of alkali, may be used either simultaneously or in this way, that the alkali earth is added first up to the finishing of the oxidation and the alkali carbonate added afterward. In the case of a diliicultly-soluble alkaline earth, such as lime, more than the equivalent proportion of the earth should be used.

Instead of sulfuric acid suitable acid sulfates such sodiurn-potassium bisulfate, niter cake, or similar eonuwunds-may be used.

1 have so .far conlined myself to the action of sulfuric acid on ferroeyanids, being the most practicable form of my process, in so far as it enables me to use lead for the distilling apparatus and to recover the alkali contained in the original ferrocyanid as sulfate, which can be made available as described above; but it is well known that if hydrochloric, phosphoric, or similar acids are used hydroeyanie have found that practically the reaction takes place in the same way as with sulfuric acid and that with hydrochloric, phosphoric, and similar acids, whatever the yield of hydrocyanic acid, the resulting Everitts salt contains exactly the amount of cyanogen corresponding to the difference between the total cyanogen originally contained in the ferrocyanid and that evolved as hydrocyanic acid in such a form that it can be practically quantitatively reeonverted into alkali :ferrocyanid.

Having now particularly described and ascertained the natureof my said invention and in what manner the same is to be performed, I declare that what 1 claim is In the manufacture of cyanids from ferrocyanids, the process herein described consisting in decomposing fcrrocyanids with a mineral acid, absorbing the hydrocyanie acid evolved in caustic alkali and reconverting the insoluble residue of metal ferro ferroeyanid obtained by the decomposition of ferrocyanids with acids, into ferrocyanid by boiling with a caustic alkali in the presence of air in excess, substantially as described.

In testimony that I claim the foregoing as my invention I have signed my name in presence of two subscribing witnesses.

JACOB GROSSMANN.

'itnesses:

WILLIAM EDGAR Sins, Janus ANDREW STEELE. 

